Biology subjects

Braeu, F. A.

Publications and source records attributed to Braeu, F. A..

3 recordsLinked to original sources

bioRxiv2025

Iris Crypts Could Reduce the Chance of Angle Closure: A Computational Biomechanics Study Derived from Clinical and Human Iris Data

PurposeTo investigate the effect of crypts during pupil constriction and dilation on the potential for angle closure by performing finite element analysis using clinical and experimental data on human tissues. MethodsA computational model was developed to determine the influence of small crypts (surface area of [~]0.015 mm2) and large crypts (surface area of 0.300 mm2) on the anterior chamber angles during pupil dilation. The model needed permeability data from human subjects, hence 21 enucleated human eyes (72 hours post-mortem) were procured and subjected to a flow set-up previously reported. Finally, 66 subjects were recruited to measure pupil constriction and dilation levels from optical coherence tomography (OCT) videos. ResultsThe hydraulic permeability of the human iris stroma was determined to be 2.55 {+/-} 1.93 x 10-5 mm2/Pa{middle dot}s. The average iris constriction and dilation durations were 0.710 {+/-} 0.213 seconds and 1.24 {+/-} 0.401 seconds, respectively, with pupil diameter changes of 1.16 {+/-} 0.39 mm and 0.75 {+/-} 0.27 mm, respectively. The computational models had starting anterior chamber angles of 51.30{degrees} and final anterior chamber angles of 26.81{degrees} once steady state has been reached. In an extreme case with decreased anterior border layer (ABL) permeability, the anterior chamber angle narrowed to 12.37{degrees}, but the presence of crypts kept the angle above 20.36{degrees}, highlighting the potential of crypts in preventing angle closure. ConclusionsOur findings on the biomechanics of crypts in the iris may drive the development of novel treatments by altering ABL morphology, providing an alternative bypass for angle closure prevention in high-risk patients.

bioengineering↗

bioRxiv2024

Iris Morphological and Biomechanical Factors Influencing Angle Closure During Pupil Dilation

PurposeTo use finite element (FE) analysis to assess what morphological and biomechanical factors of the iris and of the anterior chamber are more likely to influence angle narrowing during pupil dilation. MethodsThe study consisted of 1,344 FE models comprising of the cornea, sclera, lens and iris (stroma, sphincter and dilator tissues) to simulate pupil dilation and to assess changes in angle. For each model, we varied the following parameters: anterior chamber depth (ACD = 2 -4 mm) and width (ACW = 10-12 mm), iris convexity (IC = 0-0.3 mm), thickness (IT = 0.3-0.5 mm), stiffness (E = 4-24 kPa) and Poissons ratio (v = 0-0.3), and simulated pupil dilation. We evaluated for the change in anterior chamber angle ({bigtriangleup}{angle}) and the final dilated anterior chamber angles ({angle}f) from baseline to dilation for each parameter. ResultsThe final dilated AC angles decreased with a smaller ACD ({angle}f = 53.4{degrees}{+/-}12.3{degrees} to 21.3{degrees}{+/-}14.9{degrees}), smaller ACW ({angle}f = 48.2{degrees}{+/-}13.5{degrees} to 26.2{degrees}{+/-}18.2{degrees}), larger IT ({angle}f = 52.6{degrees}{+/-}12.3{degrees} to 24.4{degrees}{+/-}15.1{degrees}), larger IC ({angle}f = 45.0{degrees}{+/-}19.2{degrees} to 33.9{degrees}{+/-}16.5{degrees}), larger E ({angle}f = 40.3{degrees}{+/-}17.3{degrees} to 37.4{degrees}{+/-}19.2{degrees}) and larger v ({angle}f = 42.7{degrees}{+/-}17.7{degrees} to 34.2{degrees}{+/-}18.1{degrees}). The change in AC angle increased with larger ACD ({bigtriangleup}{angle} = 9.37{degrees}{+/-}11.1{degrees} to 15.4{degrees}{+/-}9.3{degrees}), smaller ACW ({bigtriangleup}{angle} = 7.4{degrees}{+/-}6.8{degrees} to 16.4{degrees}{+/-}11.5{degrees}), larger IT ({bigtriangleup}{angle} = 5.3{degrees}{+/-}7.1{degrees} to 19.3{degrees}{+/-}10.2{degrees}), smaller IC ({bigtriangleup}{angle} = 5.4{degrees}{+/-}8.2{degrees} to 19.5{degrees}{+/-}10.2{degrees}), larger E ({bigtriangleup}{angle} = 10.9{degrees}{+/-}12.2{degrees} to 13.1{degrees}{+/-}8.8{degrees}) and larger v ({bigtriangleup}{angle} = 8.1{degrees}{+/-}9.4{degrees} to 16.6{degrees}{+/-}10.4{degrees}). ConclusionsThis parametric study offered valuable insights into the factors that could influence angle closure. The morphology of the iris (IT and IC) and its innate biomechanical behavior (E and v) were crucial in influencing the way the iris deformed during dilation, and angle closure was further exacerbated by decreased AC biometry (ACD and ACW).

bioengineering↗

bioRxiv2022

The Structural Layers of the Porcine Iris Exhibit Inherently Different Biomechanical Properties

PurposeTo isolate the structural components of the ex vivo porcine iris tissue and to determine their biomechanical properties. MethodsThe porcine stroma and dilator tissues were separated, and their dimensions were assessed using optical coherence tomography (OCT). The stroma underwent flow test (n = 32) to evaluate for permeability using Darcys Law ({Delta}P = 2000 Pa, A = 0.0391 mm2), and both tissues underwent stress relaxation experiments ({varepsilon} = 0.5 with initial ramp of {delta}{varepsilon} = 0.1) to evaluate for their viscoelastic behaviours (n = 28). Viscoelasticity was characterised by the parameters {beta} (half width of the Gaussian distribution), {tau}m(mean relaxation time constant), E0 (instantaneous modulus) and E{infty} (equilibrium modulus). ResultsFor the stroma, the hydraulic permeability was 9.49 {+/-} 3.05 x 10-6 mm2/Pa{middle dot}s, and the viscoelastic parameters were {beta} = 2.50 {+/-} 1.40, and {tau}m = 7.43 {+/-} 4.96 s, with the two moduli calculated to be E0= 14.14 {+/-} 6.44 kPa and E{infty} = 6.08 {+/-} 2.74 kPa. For the dilator tissue, the viscoelastic parameters were {beta} = 2.06 {+/-} 1.33 and {tau}m = 1.28 {+/-} 1.27 s, with the two moduli calculated to be E0 = 9.16 {+/-} 3.03 kPa and E{infty} = 5.54 {+/-} 1.98 kPa. ConclusionWe have established a new protocol to evaluate the biomechanical properties of the structural layers of the iris. Overall, the stroma was permeable and exhibited smaller moduli than those of the dilator muscle. An improved characterisation of iris biomechanics may form the basis to further our understanding of angle closure glaucoma.

bioengineering↗